EP0543656B1 - Dispositif de mémoire à semi-conducteurs effaçable par bloc ayant un fonctionnement amélioré - Google Patents

Dispositif de mémoire à semi-conducteurs effaçable par bloc ayant un fonctionnement amélioré Download PDF

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Publication number
EP0543656B1
EP0543656B1 EP92310606A EP92310606A EP0543656B1 EP 0543656 B1 EP0543656 B1 EP 0543656B1 EP 92310606 A EP92310606 A EP 92310606A EP 92310606 A EP92310606 A EP 92310606A EP 0543656 B1 EP0543656 B1 EP 0543656B1
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EP
European Patent Office
Prior art keywords
memory cell
gate
voltage
cell array
flash
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP92310606A
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German (de)
English (en)
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EP0543656A3 (en
EP0543656A2 (fr
Inventor
Takao C/O Fujitsu Limited Akaogi
Yasushige c/o Fujitsu VLSI Limited Ogawa
Tatsuya C/O Fujitsu Limited Kajita
Hisayoshi c/o Fujitsu Limited Watanabe
Minoru c/o Fujitsu Limited Yamashita
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Fujitsu VLSI Ltd
Fujitsu Ltd
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Fujitsu VLSI Ltd
Fujitsu Ltd
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Priority claimed from JP30489491A external-priority patent/JP3144002B2/ja
Priority claimed from JP31668291A external-priority patent/JP2625298B2/ja
Priority claimed from JP31945191A external-priority patent/JP3106624B2/ja
Priority claimed from JP34734391A external-priority patent/JP3543973B2/ja
Priority claimed from JP421692A external-priority patent/JP3116505B2/ja
Priority claimed from JP6173092A external-priority patent/JP2689808B2/ja
Priority claimed from JP21038092A external-priority patent/JP3201838B2/ja
Priority claimed from JP24995892A external-priority patent/JPH06103798A/ja
Priority claimed from JP31047292A external-priority patent/JP3360855B2/ja
Priority to EP01109362A priority Critical patent/EP1126473B1/fr
Priority to EP01109361A priority patent/EP1126472B1/fr
Priority to EP01109363A priority patent/EP1126474B1/fr
Priority to EP97119754A priority patent/EP0841667B1/fr
Application filed by Fujitsu VLSI Ltd, Fujitsu Ltd filed Critical Fujitsu VLSI Ltd
Publication of EP0543656A2 publication Critical patent/EP0543656A2/fr
Publication of EP0543656A3 publication Critical patent/EP0543656A3/en
Application granted granted Critical
Publication of EP0543656B1 publication Critical patent/EP0543656B1/fr
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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10B—ELECTRONIC MEMORY DEVICES
    • H10B41/00—Electrically erasable-and-programmable ROM [EEPROM] devices comprising floating gates
    • H10B41/40—Electrically erasable-and-programmable ROM [EEPROM] devices comprising floating gates characterised by the peripheral circuit region
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C16/00—Erasable programmable read-only memories
    • G11C16/02—Erasable programmable read-only memories electrically programmable
    • G11C16/06—Auxiliary circuits, e.g. for writing into memory
    • G11C16/08—Address circuits; Decoders; Word-line control circuits
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C16/00—Erasable programmable read-only memories
    • G11C16/02—Erasable programmable read-only memories electrically programmable
    • G11C16/06—Auxiliary circuits, e.g. for writing into memory
    • G11C16/10—Programming or data input circuits
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C16/00—Erasable programmable read-only memories
    • G11C16/02—Erasable programmable read-only memories electrically programmable
    • G11C16/06—Auxiliary circuits, e.g. for writing into memory
    • G11C16/10—Programming or data input circuits
    • G11C16/14—Circuits for erasing electrically, e.g. erase voltage switching circuits
    • G11C16/16—Circuits for erasing electrically, e.g. erase voltage switching circuits for erasing blocks, e.g. arrays, words, groups
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C16/00—Erasable programmable read-only memories
    • G11C16/02—Erasable programmable read-only memories electrically programmable
    • G11C16/06—Auxiliary circuits, e.g. for writing into memory
    • G11C16/30—Power supply circuits
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C16/00—Erasable programmable read-only memories
    • G11C16/02—Erasable programmable read-only memories electrically programmable
    • G11C16/06—Auxiliary circuits, e.g. for writing into memory
    • G11C16/32—Timing circuits
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C29/00—Checking stores for correct operation ; Subsequent repair; Testing stores during standby or offline operation
    • G11C29/70—Masking faults in memories by using spares or by reconfiguring
    • G11C29/78—Masking faults in memories by using spares or by reconfiguring using programmable devices
    • G11C29/84—Masking faults in memories by using spares or by reconfiguring using programmable devices with improved access time or stability
    • G11C29/846—Masking faults in memories by using spares or by reconfiguring using programmable devices with improved access time or stability by choosing redundant lines at an output stage
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10B—ELECTRONIC MEMORY DEVICES
    • H10B41/00—Electrically erasable-and-programmable ROM [EEPROM] devices comprising floating gates
    • H10B41/40—Electrically erasable-and-programmable ROM [EEPROM] devices comprising floating gates characterised by the peripheral circuit region
    • H10B41/42—Simultaneous manufacture of periphery and memory cells
    • H10B41/43—Simultaneous manufacture of periphery and memory cells comprising only one type of peripheral transistor
    • H10B41/48—Simultaneous manufacture of periphery and memory cells comprising only one type of peripheral transistor with a tunnel dielectric layer also being used as part of the peripheral transistor
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10B—ELECTRONIC MEMORY DEVICES
    • H10B69/00—Erasable-and-programmable ROM [EPROM] devices not provided for in groups H10B41/00 - H10B63/00, e.g. ultraviolet erasable-and-programmable ROM [UVEPROM] devices

Definitions

  • the present invention generally relates to semiconductor devices and more particularly to a flash-erasable EPROM device or simply a flash memory device that has an improved reliability.
  • FIG.1 shows the structure of a typical memory cell transistor that forms a flash memory device.
  • the memory cell transistor is constructed on a semiconductor substrate 1 and includes a source region 6 and a drain region 7 formed in the substrate 1 similarly to a conventional MOS transistor.
  • a gate insulation film 2 is provided to cover the channel region extending between the source region 6 and the drain region 7, and a gate electrode 3 is formed on the gate insulation film 2 in correspondence to the channel region of the device.
  • a capacitor insulation film 4 in provided to surround the gate electrode 3, and the gate electrode 3 thereby forms a floating gate electrode.
  • an electrode 5 is provided on the floating gate electrode 3 such that the electrode 5 is insulated from the electrode 3 by the capacitor insulation film 4. Thereby, the electrode 5 is used an a control electrode.
  • a predetermined drive voltage is applied across the source region 6 and the drain region 7 such that the electrons are caused to flow from the source region 6 to the drain region 7.
  • a large positive voltage is applied to the control electrode 5 to induce a large electric field between the floating gate electrode 3 and the substrate 1.
  • the electrons transported along the channel region and accelerated in the vicinity of the drain region 7 are injected into the floating gate electrode 3 through the gate insulation film 2 as hot electrons.
  • the electric charges associated with the electrons controls the conduction of the channel region between the source and drain regions 6 and 7. In other words, one can read the content of the data written into the memory cell transistor by detecting the conduction thereof.
  • FIG.2 shows the foregoing control scheme of the flash memory device for the writing mode for wiring data into the memory cell, the reading mode for reading data from the memory cell, and the erasing mode for erasing data from the memory cell, wherein the voltage V H in set typically to +12 volts, while the voltage V M may be set to +6 volts. Further, the voltage V L is set to about +5 volts.
  • FIG.3 shows the overall construction of a typical flash memory device.
  • the device includes a memory cell array 11 in which a plurality of memory cell transistors each having a construction of FIG.1 are arranged in rows and columns, and the memory cell in the memory cell array 11 is selected in response to address data that is supplied to a row address buffer circuit 12 for activating a row decoder 13 and a column address buffer circuit 14 for activating a column decoder 15.
  • the row decoder 13 selects a word line WL in response to the row address data latched in the row address buffer circuit 12 while the column decoder 15 controls a column selection gate 16 to select a bit line BL in response to the column address data that is latched in the column address buffer circuit 14.
  • a data bus 17 connected to an input/output buffer circuit 18, and the data on the bus 17 is written into a selected memory cell such as the memory cell 11a via a write amplifier 19 and the column selection gate 16.
  • the data stored in the selected memory cell is transferred to the input/output buffer circuit 18 via the column selection gate 16 and a sense amplifier 20.
  • another buffer circuit 21 that is supplied with an output enable signal /OE, a chip enable signal /CE, and further with a write enable signal /WE, wherein the signal /OE is used for enabling the data output of the input/output buffer circuit 18, the signal /CE is used for the chip selection, and the signal /WE is used for enabling the writing of data into the selected memory cell.
  • an erase power supply unit 22 that characterizes the NOR type flash memory device, wherein the power supply unit 22 supplies a predetermined erase voltage when erasing the data from the memory cell array. As is well known, the erasing of data occurs simultaneously for all the memory cells in the memory cell array 11 in the flash memory device.
  • a controller 23 is provided in order to control the operation of memory cell device including the erase power supply 22. There, the controller 23 is supplied with data from the data bus 17 as well as an output of the buffer circuit 21 and controls the read/write as well as erase operation of the device.
  • FIG.4 shows the writing of data into the memory cell transistor of FIG.1, wherein the vertical axis represents the drain current and the horizontal axis represents the drain voltage.
  • the voltage V D is applied to the drain region during the writing process of data, while the voltage V H is applied simultaneously to the control gate.
  • the drain current increases in an interval designated as "1" with increasing drain voltage V D , while the drain current decreases suddenly in correspondence to the interval designated as "2" with further increase in the drain voltage V D .
  • the injection of electrons into the floating gate electrode occurs.
  • an avalanche voltage V ABD an avalanche breakdown occurs in the channel region of the memory cell transistor and the drain current increases steeply. Thereby, an efficient injection of the electrons is achieved into the floating gate.
  • the flash memory device generally uses the avalanche voltage V ABD for the voltage V M shown in FIG.2 to achieve an efficient writing of the data.
  • the drain voltage V D is clamped at the level V ABD when the foregoing positive control voltage V H is applied to the control gate.
  • the drain current changes as shown in the broken line in FIG.4.
  • the drain current remains low until a breakdown voltage V JCT is reached.
  • V JCT is larger than V ABD by more than one volt.
  • the large drain voltage applied to the first memory cell transistor for writing data induces a large electric field between the drain region and the floating gate in the second memory cell transistor.
  • the electric charges stored in the second memory cell transistor can dissipate into the drain of the same memory cell transistor and the data held therein is destroyed. This interference of memory cell transistors is known as disturbance.”
  • the conventional flash memory device has suffered from the problem of limited flexibility in the design of redundant construction in that only the column redundancy is possible as shown in FIG.5.
  • the drawing corresponds to FIG.3 and includes the memory cell array 11 that in turn includes a number of memory cells M 1,1 - M 2,3 provided in correspondence to intersections of word lines WL 1 - WL 2 and bit lines BL 1 - BL 3 .
  • the column selection gate 16 includes transfer gate transistors Tsw 1 - Tsw 3 for selecting the bit lines BL 1 - BL 3 respectively.
  • the redundant memory cell array 11 CR includes memory cell transistors M 1,4 and M 2,4 having respective drains connected commonly to the bit line BL 4 and the memory cell array 11 CR is activated in response to the output of the redundant decoder 24 that in turn is controlled by a defect detection circuit 25.
  • the circuit 25 is supplied with the column address data from a column buffer circuit 14 and compares the same with the address data for defective memory cells stored in a memory device not illustrated.
  • the circuit 25 activates the redundant decoder 24 that in turn selects the redundant bit line BL 4 .
  • a redundant memory cell array may be provided as a part of a utility memory cell array that is provided separately from the real memory cell array for various purposes such as testing. In other words, one can use such a memory cell array 11 CR also for testing as will be discussed later with reference to the embodiment of the present invention.
  • the electric charges are removed from the floating gate each time the data stored in the memory cell is erased.
  • such an erasing process is conducted by applying a positive voltage to the source region.
  • all the memory cells that are connected commonly to the source supply voltage experience dissipation of the electric charges from the floating gate.
  • the data stored in the memory cells that form the memory cell array of the device are erased simultaneously.
  • the floating gate is injected with holes and the memory cell transistors take a permanently turned-on state.
  • the transistors M 1,1 -M 1,4 are connected to the bit lines BL 1 - BL 4 , such an erroneous turning-on of the memory cell transistors inevitably causes a erroneous voltage level of the bit lines and the overall operation of the flash memory device becomes defective.
  • a utility memory cell block for testing the device
  • Such a utility block is used for example for the purpose of guaranteeing a predetermined number of times for the rewriting of data into the memory cell transistors forming the memory cell array.
  • erasing of data is achieved in the ordinary, "real" memory cell block each time the data is erased from the utility memory cell block, as long as the memory cell transistors in the real memory cell block share the electric power supply with the memory cell transistors in the utility memory cell block. Thereby, the memory cell transistors in the real memory cell block are erased excessively and the proper read/write operation of the device is no longer possible.
  • the conventional flash memory devices have suffered from the problem that the test for guaranteeing the number of times the write operation can be achieved properly is impossible.
  • EP-A-0 392 895 An example of a conventional flash memory is disclosed in EP-A-0 392 895. This document describes a flash EEPROM in which any combinations of flash sectors may be erased together.
  • Another object of the present invention is to provide a flash memory device that makes a row-redundant construction possible. As a result of the row-redundancy, the degree of freedom for realizing the redundancy is substantially increased.
  • a flash-erasable semiconductor memory device comprising: a memory cell array including a plurality of memory cell transistors, each of said memory cell transistors comprising: an insulated floating gate provided on a semiconductor substrate with a separation therefrom for storing information in the form of electric charges; a gate insulation film provided on an upper major surface of said semiconductor substrate for separating said floating gate from said semiconductor substrate; a channel region defined in said semiconductor substrate in correspondence to said floating gate; a source region and a drain region defined in said semiconductor substrate at both sides of said floating gate, said source region injecting carriers into said channel region such that said carriers are transported along said channel region while said drain region collecting carriers that have been injected into said channel region at said source region and transported through channel region; and a control electrode provided on said floating gate, separated therefrom by a capacitor insulation film for controlling an injection of carriers from said channel region to said floating gate via said gate insulation film; addressing means supplied with address data for selecting a memory cell transistor in said memory cell array; writing means for writing information into said selected memory cell
  • FIG.6 shows the principle of a flash memory to which the present invention may be applied.
  • the flash memory includes the memory cell array schematically illustrated in the form of the memory cell transistor 11a, wherein the control circuit 23 of the flash memory as represented schematically in FIG.3 includes a signal generator 233 that is supplied with an output signal PGM of the buffer circuit 21 in response to the write enable signal /WE when writing data. There, the circuit 233 produces a first control signal PGMR and a second control signal PGMC in response to the signal PGM, wherein the signal PGM causes a transition to the high level state during the interval in which the writing of data is achieved.
  • the circuit 231 in turn produces a gate voltage V G in response to the signal PGMC and the voltage level of the control gate represented as "G" in FIG.6 is held at a high level state corresponding to the voltage V H during the interval in which the signal PGMC assumes the high level state.
  • the circuit 232 in turn produces a drain voltage represented as V D in FIG.6 such that the drain voltage V D is held at the level V M during the high level interval of the signal PGMC.
  • the gate voltage V G is set to the high level state V H before the drain voltage V D rises to the high level state V M , and the gate voltage V G maintains the high level state even after the drain voltage V D has caused a transition to the low level state.
  • FIG.7 shows the circuit diagram of the circuit 233.
  • the circuit 233 includes an inverter 233a supplied with the signal PGM and produces an output as a logic inversion of the signal PGM.
  • the output of the inverter 233a is supplied on the one hand to a AND gate 233d and on the other hand to a NOR gate 233e, wherein the NAND gate 233d and the NOR gate 233e form a flip-flop circuit that includes a first feedback path for feeding back the output of the NAND gate 233d to another input terminal of the NOR gate 233e via an inverter 233b and a second feedback path for feeding back the output of the NOR gate 233e to another input terminal of the NAND gate 233d via an inverter 233c.
  • FIGS.8(A) - 8(C) show the output signals PGMR and PGMC with a timing relationship as shown in FIGS.8(A) - 8(C), wherein FIG.8(A) shows the waveform of the signal PGM, FIG.8(B) shows the waveform of the signal PGMR, and FIG.8(C) shows the waveform of the signal PGMC.
  • PGMR rises substantially in synchronization to the leading edge of the PGM, while the leading edge of the PGMC is delayed with respect to the leading edge of the PGM by an interval td 1 , wherein the interval td 1 corresponds to the delay caused by the NAND gate 233d and the inverter 233b.
  • the delay td 1 is set such that the rise of the drain voltage V D occurs after the rise of the gate voltage V G in the circuit 233 of FIG.7
  • the PGMC causes a transition to the low level state substantially in synchronization with the trailing edge of the PGM, while the trailing edge of the PGMR appears after a delay of td 2 with respect to the trailing edge of the PGM, wherein the delay td 2 is determined by the delay caused by the NOR gate 233e and the inverter 233c.
  • the delay td 2 is determined such that the gate voltage returns after the drain voltage returns to the low level state.
  • FIG.9 is a block diagram similar to FIG.5 and shows the construction of the memory device that uses the foregoing circuit 233 for the formation of the signals PGMR and PGMC.
  • those parts corresponding to FIG.5 are designated by the same reference numerals and the description will be omitted.
  • the PGMR is supplied to a row selection power supply circuit 13A that produces the output signal V G in response to the high level state of the PGMR, and the signal V G is supplied to the row decoder 13 to which the row address data is supplied simultaneously.
  • the row decoder 13 selects a word line such as WL 1 in response to the row address data supplied thereto and supplies the gate voltage V G to the selected word line WL 1 .
  • a column power supply circuit 15A that is supplied with the PGMC, wherein the circuit 15A activates the column decoder 15 in response to the high level interval of the PGMC.
  • the PGMC is supplied also to a drain power supply circuit 19A that forms a part of the write amplifier 20, and the drain voltage V D is controlled as already described with reference to FIGS.8(A) - 8(C) in response to the PGMC.
  • the drain voltage V D never increases beyond the avalanche voltage V ABD , and the problem of the disturbance is successfully eliminated.
  • the delay times td 1 and td 2 are determined to be larger than the difference between the signal delay occurring in the conductor strip that transfers the signal PGMR from the circuit 233 to the control gate of the selected memory cell transistor and the signal delay occurring in the conductor strip for transferring the signal PGMC from the circuit 233 to the drain region of the selected memory cell transistor.
  • the conductor strip used for carrying the signal PGMR is generally formed of polysilicon and the delay occurring in the conductor strip for transferring the signal PGMR is generally larger than the delay occurring in the conductor that transfers the signal PGMC.
  • FIG.10 wherein the present embodiment relates to the flash memory device having the row redundancy.
  • FIG.10 those parts corresponding to the parts already described with reference to FIG.5 or FIG.9 are designated by the same reference numerals and the description thereof will be omitted.
  • the memory cell array 11 includes a row and column formation of the real memory cell transistors M 1,1 - M 3,3 that are selected by the row decoder 13 and the column decoder 15 similarly to the embodiment of FIG.5, wherein it will be noted that there is provided an additional memory cell block that includes memory cell transistors M 3,1 - M 3,3 also in the memory cell array 11 as a row redundant memory cell block, and a defect detection circuit 34 for detecting the selection of a defective word line and a redundant word decoder 35 for selecting a redundant word line such as WL 3 in response to the output of the defect detection circuit 34, are provided for activating the row redundant memory cell block.
  • the phrase "defective word line” means a word line to which a defective memory cell transistor is connected.
  • an additional, utility memory cell block connected to a word line WL 4 that is selected by a utility word decoder 36.
  • the utility memory cell block includes memory cell transistors M 4,1 - M 4,3 and is used for testing the operation of the flash memory device.
  • the present embodiment in order to avoid the problem of the excessive erasing of information from non-selected memory cells described previously in relation to the problem of row redundancy in the flash memory devices as well as the problem of the erase disturbance phenomenon, the present embodiment employs a construction to apply a large negative voltage -V E selectively to the control electrode of the memory cell transistor from which the information is to be erased, such that a dissipation of the electrons occurs from the floating gate to the substrate as indicated in FIG.11. There, a positive voltage V L corresponding to the voltage V L described with reference to FIG.2 is applied to the substrate of the device.
  • a zero or positive voltage is applied to the control electrode of the non-selected memory cells to avoid dissipation of the electric charges from the floating gate of the non-selected memory cells to the substrate.
  • the voltage V E is set to -9 volts.
  • the dissipation of the electrons may be caused from the floating gate to the source region by applying the voltage V E to the control gate and the voltage V L to the source simultaneously as indicated in FIG.12.
  • the present embodiment shown in FIG.10 employs a construction of the row address buffer circuit 12 as shown in FIG.13, wherein only a part of the circuit is illustrated. It should be noted, on the other hand, that the power supply 22 is no longer used for the erasing purpose. Thus, the power supply 22 merely produces zero volt or a voltage corresponding to the level V H .
  • the circuit 12 includes a NOR gate 12a that is supplied on the one hand with a control signal PD that is set to the low level state during the operational state of the flash memory device and on the other hand with an address signal included in the multiple-bit address data, wherein the output of the NOR gate 12a is supplied to a first input terminal of another NOR gate 12c via an inverter 12b. Further, the output of the NOR gate 12a is supplied to an input terminal of a NOR gate 12d.
  • both the NOR gate 12c and the NOR gate 12d are supplied with an output of the defect detection circuit 34 simultaneously, wherein the defect detection circuit 34 produces the output such that the output of the circuit 34 assumes a high level state when a selection of the defective word line is made.
  • the output of the circuit 34 is of course set to the low level state.
  • both the output signal AD of the NOR gate 12c and the output signal /AD of the NOR gate 12d are set to the low level state. It should be that the circuit of FIG.13 is provided in number corresponding to the number of the bits of the address data to form the address buffer circuit 12.
  • FIG.14 shows the construction of the row decoder 13, wherein the row decoder 13 includes a NAND gate 13a that receives the address data from the row address buffer circuit 12.
  • the output of the row decoder 13 is supplied, via an n-channel MOS transistor 13b and a p-channel MOS transistor 13g both urged to a turned-on state by the supply voltages V cc and V ss respectively, to a latch circuit that includes a p-channel MOS transistor 13h and an n-channel MOS transistor 13c connected in series between a power supply voltage V DD2 and another power supply voltage V DS2 .
  • the latch circuit further includes a p-channel MOS transistor 13i and an n-channel MOS transistor 13d connected in series between the foregoing power supply voltages V DD2 and V DS2 , wherein the transistors 13h and 13i as well as the transistors 13c and 13d are connected such that the voltage at the node between the transistors 13h and 13c is supplied to the respective gates of the transistors 13i and 13d and such that the voltage at the node between the transistors 13i and 13d is supplied to the respective gates of the transistors 13h and 13c.
  • the output of the latch circuit is obtained at the node between the transistors 13i and 13d and is supplied to the gate of an n-channel MOS transistor 33e that is connected in series to another n-channel MOS transistor 13f.
  • the transistors 13e and 13f are connected in series between a supply voltage V DS1 and a supply voltage V DS2 , wherein the transistor 13f is supplied with the output of the transistor 13g directly.
  • the voltage V cc is typically set to +5 volts while the voltage V ss is set typically to zero volt.
  • the voltages V DD1 and V DS2 are set, in the erasing mode, to the foregoing negative voltage V E that is applied to the control gate of the memory cell transistor for erasing data therefrom.
  • the voltages V DD2 and V DS1 correspond to the voltage V L that is supplied to the substrate in the erasing scheme of FIG.11. In the erasing mode shown in FIG.12, the voltage V L is supplied to the source region.
  • the circuit of FIG.14 outputs the control voltage on the selected word line WL i such that the control voltage is set to the level V E in the erasing mode.
  • the NAND gate 13a produces a low level output in response to the address data that selects the word line WL i .
  • the NAND gate 13a produces a high level output and a control signal having the level V L is outputted on the non-selected word line in response thereto.
  • a similar construction is used for the row redundant word line decoder 35 and the utility word line decoder 36.
  • the NAND gate 13a is replaced by an inverter 13j that is supplied with the output signal from the defect detection circuit 34.
  • an inverter 13k is used in place of the NAND gate 13a in the utility word line decoder 36, wherein the inverter 13k produces an output in response to a test signal supplied thereto.
  • the redundant word line WL 3 shown in FIG.10 is selected and the voltage level of the redundant word line WL 3 is urged to the level V E in correspondence to the supply voltage V DD1 when erasing data.
  • the rest of the word lines are all urged to the voltage V L in correspondence to the supply voltage V DS1 .
  • the flash erasing operation applied to the row redundant memory cell block does not cause the adversary erasing in the real memory cell block.
  • the utility memory cell block connected to the word line WL 4 can be achieved independently from the rest of the memory cells and the problem of the excessive erasing is eliminated.
  • FIG.15 shows a circuit 13X for causing the foregoing change of the supply voltage V DD1 in response to the operational mode of the flash memory device.
  • the circuit 13X forms a part of the circuit 13 we well as 35 and 36 in the illustration of FIG.10 and includes a p-channel transistor 191 having a source connected to the supply voltage V CC and a p-channel transistor 192 connected in series to the transistor 191. Further, there is provided a p-channel transistor 193 having a source connected to the supply voltage V PP and another p-channel transistor connected in series to the transistor 193. The respective sources of the transistors 192 and 195 are connected commonly to another p-channel transistor 195 that is turned on in response to the erase control signal E. There, the transistors 191 and 192 have respective gates supplied with the write control signal W while the transistors 193 and 194 have respective gates supplied with the complementary write control signal /W.
  • the transistors 191 and 192 are turned on while the transistors 193 and 194 are turned off, and the supply voltage V CC is supplied to the transistor 195.
  • the control signal E takes a low level state and the supply voltage V CC thus supplied via the transistors 191 and 192 is supplied further through the transistor 195 to the supply terminal V DD1 of the circuit 13 shown in FIG.14.
  • the transistors 193 and 194 are turned on while the transistor 191 and 192 are turned off, and the high positive supply voltage Vpp is supplied to the terminal V DD1 via the transistor 195 that is turned on in response to the non-erasing mode.
  • the circuit of FIG.15 includes a number of p-channel transistors 196, 197, 198, ... connected to form a diode wherein the transistors 196, . . . are connected in series to the supply voltage V SS via an n-channel transistor 195A that is turned on and turned off in response to the erase control signal E.
  • the transistor 195A is turned off in response to the low level state of the control signal E, and the transistors 196, 197, 198, . . . are disconnected from the supply voltage V SS .
  • the signal E takes a high level state and the transistor 195 turns off while the transistor 195A is turned on.
  • the supply voltage V SS is supplied after voltage drop caused by the diode connection of the transistors 196, . . . and a large negative voltage corresponding to V E appears at the terminal V DD1 of the circuit 13 of FIG.14.
  • the transistors 196, 197, ... . are supplied with a clock signal ⁇ and a logic inversion / ⁇ .
  • FIG.16 shows a device that has a column redundancy.
  • FIG.16 those parts described previously are designated by the same reference numerals and the description thereof will be omitted.
  • the memory cell array 11 is divided into a number of memory cell blocks 11 1 ... 11 m , wherein each memory cell block has a corresponding erase power supply 22 1 , ... 22 m for supplying the source drive voltage of the flash memory cells such that the flash-erasing of information occurs in each memory cell block independently.
  • a redundant memory cell column 11 CR corresponding to the column redundant memory cell array shown in FIG.5, and the redundant memory cell column 11 CR receives the source drive voltage from an independent erase power supply 22 CR . Similar to the device of FIG.5, the redundant memory cell block 11 CR is selected in response to the output from the defect detection circuit 25.
  • the redundant decoder 24 is included in the column decoder 15.
  • each of the memory cell blocks 11 1 - 11 m includes only the real memory cells. In other words, the memory cell blocks 11 1 - 11 m does not include the redundant memory cell column or utility memory cell column.
  • FIG.17 is a circuit diagram showing a part of the device of FIG.16 in detail.
  • those parts described previously are designated by the same reference numerals and the description will be omitted.
  • bit lines such as the bit lines BL 1 - BL n are grouped to form a memory cell block such as 11 1 , ... 11 m wherein no redundant memory cell column is included in each memory cell block.
  • each memory cell block is activated by a corresponding power supply unit such as 22 1 , . . . 22 m via source supply lines SL 1 - SL m and the flash-erasing or simultaneous erasing of information is achieved within each memory cell block.
  • the area that in occupied by the redundant memory cell column can be reduced as compared with the conventional redundant construction wherein the redundant memory cell column is provided in each of the memory cell blocks.
  • the erasing of the redundant memory cell block 11 CR does not cause the problem of the excessive erasing in the real memory cell array 11.
  • FIG.18 shows a modification of the device of FIG.16 wherein the memory cell array 11 is formed of a single row and column formation of the memory cell transistors M 1,1 - M m,m , wherein the device further includes the utility memory cell column 11 UT .
  • the utility memory cell column 11 UT includes memory cells M 1,U , M 2,U , ..., wherein each of the memory cells M 1,U , ... have the source region connected commonly by a source supply line SL U to the power supply unit 22 UT that is provided independently from the power supply unit 22 that supplies the source voltage to the memory cell transistors in the memory cell array 11.
  • the power unit 22 UT changes the supply voltage in response to the operational mode particularly in the erasing mode as already described with reference to the basic operation of the flash memory device such that the supply voltage is changed independently to the supply voltage that is supplied to the source of the memory cell transistors M 1,1 - M m,m from the power supply unit 22.
  • the utility memory cell column 11 UT of FIG.18 may be used for example for the testing purpose for guaranteeing the number of times the device is capable of rewriting as already described, wherein the device of FIG. 16 is advantageous in the point that the erasing operation of the utility memory cell column 11 UT does not affect at all the state of the real memory cell array 11 because of the use of the separate, independent power supply unit 22 UT for effecting a connection of the bit line BL U to the sense amplifier 20.
  • a test control signal is supplied to the gate of the column gate transistor (Tsw) UT .
  • FIG.19 wherein those parts corresponding to the parts described previously are designated by the same reference numerals and the description will be omitted.
  • the memory cell array 11 is divided into a plurality of memory cell blocks 11 1 - 11 m , wherein the device further includes a redundant memory cell column 11 CR and a utility memory cell column 11 UT .
  • Each memory cell block includes a plurality of bit lines connected commonly to a source of a MOS transistor that forms the switch S 1 to be described below.
  • the memory cell blocks 11 1 - 11 m as well as the memory cell columns 11 CR and 11 UT are connected to the sense amplifier 20 and the write amplifier 19 via a common output line DL wherein there are provided switches SW 1 - SW CR for controlling the connection between the bit lines in the memory cell blocks 11 1 - 11 m and the output line DL as well as the connection between the bit lines included in the memory cell columns 11 UT and 11 CR and the output line DL.
  • the switches SW 1 - SW CR are supplied with a control signal S 1 - S CR and are activated in response thereto.
  • each of the memory cell blocks and memory cell columns 11 1 - 11 CR has a corresponding power supply unit 22 1 - 22 CR for supplying the source voltage to the memory cell transistors included therein.
  • the power supply units 22 1 - 22 CR are designed to have respective output power or supply current that is optimized based upon the number of the memory cells included in the corresponding memory cell block or memory cell column.
  • the optimization of the current output ability of the power supply units will be described in brief.
  • the erasing of information is achieved by removing the electric charges from the floating electrode gate in the form of tunneling current.
  • the holes are created as a result of formation of the tunneling current and the holes thus created penetrate into the gate insulation film located under the floating gate.
  • the operational characteristics of the memory cell transistor is deteriorated.
  • such an accumulation of the holes in the gate insulation film is one of the major reasons that limits the lifetime of a flash memory device.
  • FIG.20 shows the change of the source current with the source voltage applied to the memory cell transistor shown in FIG.1 during the erasing operation, wherein FIG.21 shows the condition that the erasing characteristics of FIG.20 is obtained.
  • the memory cell transistor shown in FIG.1 is biased according to the erasing condition an set forth in FIG.2, and a gate current that flows from the floating gate 3 to the source 6 is measured by applying a d.c. voltage to the floating gate.
  • the source current I S increases gradually with increasing source voltage V S until a critical voltage V SC is reached above which the source current I S increases steeply due to the avalanche breakdown.
  • the erasing of the information is achieved during this interval where the source current I S increases gradually with the source voltage V S .
  • the critical voltage V SC is attained, it will be noted that a gate current starts to flow from the floating gate electrode 3 to the source region 6 as indicated in FIG.20.
  • the optimization of the source current is essential in each of the memory cell blocks and the memory cell columns in the configuration as shown in FIG.19.
  • the utility memory cell column 11 UT in particular, it is essential to supply the source voltage such that the same source current flows in each memory cell transistor therein during the erasing operation as in the memory cell transistors in the memory cell blocks 11 1 - 11 m . Otherwise, the result of the rewriting test conducted on the utility memory cell column becomes useless.
  • FIGS.22(A) - 22(D) show the construction of the power supply units 22 1 - 22 UT , wherein the circuits shown therein have generally a similar connection.
  • the power supply unit 22 1 has an input terminal 22a to which an erase control signal ERS3 is supplied.
  • the erase control signal ERS3 thus supplied is further transferred to the gate of a p-channel MOS transistor 22d and an n-channel MOS transistor 22c connected in series between a supply voltage source V PP and the ground via a transfer gate transistor 22b that is urged to the turned-on state by a supply voltage V CC supplied to the gate thereof.
  • the output obtained at the intermediate node between the transistors 22c and 22d is supplied on the one hand to the gate of a p-channel MOS transistor 22c that is connected between the supply voltage source and a node 22g connected to the gate of the transistors 22c and 22d, and on the other hand to the gate of the transistors 22h and 22j that are connected in series between the power supply V PP and the ground with a transistor (22i) 1 interposed therebetween.
  • the transistor (22i) 1 has a gate and a source connected with each other to form a constant current circuit, and the output of the circuit 22 1 is obtained at the node where the transistor (22i) 1 is connected to the transistor 22 j .
  • the output transistor (22i) 1 has a gate width W 1 that is adjusted to supply an optimized output current to the source line SL 1 that is connected to the source of the memory cell transistors.
  • the node 22g takes a low level state in response to the low level state of the erase control signal ERS 1 that indicates the non-erasing mode, and the p-channel transistor 22d is turned on while the n-channel transistor 33c is turned off. Thereby, the node 22f is urged to the level V PP and the p-channel transistors 22e and 22h are turned off while the n-channel MOS transistor 41 is turned on. As a result, the source line SL 1 is set to zero volt.
  • the erase signal ERS 1 is set to the high level state in correspondence to the erasing operation, on the other hand, the level of the node 22g is urged to the Vcc level and the transistor 22c is turned on. As a result, the level of the node 22f approaches to zero and the p-channel transistors 22e and 22h are turned on while the n-channel transistor 22j is turned off.
  • the level of the node 22g rises to the level V PP , and the p-channel transistor 22d is turned off.
  • the level of the node 22f is urged to zero volt and the supply voltage V PP is supplied to the source line SL 1 via the p-channel transistor 22h and the n-channel transistor (22i) 1 .
  • the erasing of information is achieved.
  • a similar operation is achieved in the other circuits shown in FIGS.20(B) - 20(D). As the operation for these circuits is obvious, further description for the supply circuits of FIGS.20(B) - 20(D) will be omitted.
  • the transistor (22i) 1 acting as a constant current source has a gate width W 1 that is set to provide a source current that is sufficient to erase the information from the memory cell transistors included in the memory cell block 11 1 .
  • the gate width W 1 is set in accordance with the number of the memory cell transistors that are included in the memory cell block. More specifically, the gate width W 1 is set such that the power supply circuit 22 1 has a capability of supplying the current I SC corresponding to the critical source voltage V SC to each of the memory cell transistors included in the memory cell block 11 1 . See FIG.20. Thereby, an optimum source current is supplied to the memory cell transistors in the memory cell block 11 1 when erasing information.
  • the output transistors (22i) m , (22i) UT and (22i) CR have respective optimum gate widths W m , W UT and W CR .
  • N 1 , N m , N UT and N CR respectively represent the number of the memory cell transistors that are included in the memory cell blocks 11 1 and 11 m and in the memory cell columns 11 UT and 11 CR .
  • FIG.23 shows the principle of this device.
  • the flash memory device employs the redundant memory cell block 11 CR and the utility memory cell block 11 UT , wherein each of the blocks 11 CR and 11 UT include a plurality of memory cells arranged to form a matrix.
  • the memory cell blocks 11 CR and 11 UT include a number of memory cell columns.
  • the column decoder 15 is provided commonly to the memory cell blocks 11 CR and 11 UT for selecting a column selection line such as BL 1 , wherein the selection of the column selection line BL 1 is achieved simultaneously in the memory cell block 11 CR and 11 UT .
  • the information read out from the selected memory cell column is supplied to the sense amplifier 20 either via a switch circuit SW 1 or SW 2 , wherein the switch circuit SW 1 is closed when the redundant memory cell block 11 CR is activated.
  • the switch circuit SW 2 is closed.
  • the output of the memory cell block 11 UT and the memory cell block 11 CR is supplied to the sense amplifier 20 selectively.
  • FIG.24 shows a more detailed representation of the circuit of FIG.23.
  • the redundant memory cell array 11 CR includes memory cell transistors M CR (1,1), ... arranged in rows and columns while the utility memory cell array 11 UT includes memory cell transistors M UT (1,1), ....
  • the redundant memory cell transistors M CR (1,1), ... are connected to column lines (CL 1 ) CR , .... while the utility memory cell transistors M UT (1,1), ... are connected to column lines (CL 1 ) UT .
  • the column lines (CL 1 ) CR , ... are selected by column gate transistors (Tsw1) CR , ...
  • the drains of the column gate transistors are connected to a common drain line (DL) CR and a common drain line (DL) UT , wherein the drain line (DL) CR is connected to the sense amplifier 20 via a transfer gate transistor Tr 1 that is supplied with a control signal RED for activating the redundant memory cell array and acts as the switch SW 1 , while the drain line (DL) UT is connected to the sense amplifier 20 via a transfer gate transistor Tr 2 that is supplied with a control signal TEST for activating the testing in the utility memory cell array and acts as the switch SW 2 .
  • the control signal RED is produced in response to the column address data upon the selection of a defective bit line. See for example the circuit of FIG.5, wherein the signal RED is produced by the redundant decoder 24.
  • the control signal TEST is produced externally upon the running of the test procedure.
  • the memory cell transistors are selected simultaneously in the redundant memory cell array 11 CR and the utility memory cell array 11 UT , wherein the information signals thus read out from the selected memory cell transistors are selected further by the transistors Tr 1 and Tr 2 in response to the control signals RED and TEST supplied thereto.
  • control signals RED and TEST are supplied also to the column driver 15a via an OR gate 15b for activating the same.
  • FIG.25 shows the construction of the OR gate 15b as a part of the driver circuit 15a.
  • the driver circuit 15a includes a number of circuit blocks 40 0 - 40 3 provided in correspondence to the column selection lines BL 1 - BL 4 , wherein each of the circuits blocks 40 0 - 40 3 have the same construction and only the circuit block 40 0 will be described.
  • the circuit block 40 0 includes a depletion mode n-channel MOS transistor 41 0 and an enhancement mode n-channel MOS transistor 43 0 connected in series, wherein the drain of the transistor 41 0 is connected to the supply voltage V cc , while the source and drain of the transistor 41 0 are connected to each other at a node 47 0 . Further, a selection signal /(A n + A m ) produced as a result of the decoding in the decoding part of the column decoder 15 is supplied to the gate of the transistor 43 0 , wherein the transistor 43 0 has a source that is connected to the ground either via a transfer gate transistor 45 or the transfer gate transistor 46.
  • the transistors 45 and 46 form a part of the OR gate circuit 15b.
  • the transistor 45 or 46 is turned on and the transistor 43 0 supplies an output signal to the foregoing node 47 0 in response to the selection signal /(A n + A n+1 ) supplied to the gate of the transistor 43 0 , provided of course that the transistor 45 or 46 is turned on.
  • the output signal at the node 47 0 is supplied further to the gate of the p-channel transistor 42 0 and simultaneously to the gate of the n-channel transistor 44 0 connected in series thereto, wherein the transistors 42 0 and 44 0 form an output stage circuit of the circuit block 40 0 and connected between the supply voltage V cc and the ground. There, the output stage circuit outputs the column selection signal on the column selection line BL 1 that is connected to the intermediate node between the transistors 42 0 and 44 0 .
  • each of the circuit blocks 40 1 - 40 3 conducts the same operation in response to various combinations of the input signals such as /(/A n + A n+1 ), /(A n + /A n+1 ) and /(/A n + /A n+1 ), wherein the drain of the transistors 43 0 - 43 3 are connected commonly to the transistors 45 and 46.
  • the area of the semiconductor chip that has been occupied by the column decoder can be reduced substantially, as the redundant memory cell array 11 CR and the utility memory cell array 11 UT use the same column decoder. Further, it should be noted that this feature is not only valid in the flash memory devices but also to other conventional semiconductor memories such as dynamic random access memories.
  • FIG.26 corresponds to a modification of the construction of the circuit of FIG.5.
  • the circuit shown here is intended for testing the erasing operation of the flash memory device and includes a write control circuit 25a.
  • the conventional circuit of FIG.5 selects a redundant memory cell column when a defective memory cell column is addressed. Thereby, the writing of the defective memory cell column is not made and the memory cells included in the defective memory cell column become excessively erased state upon the flash-erasing process. In the circuit of FIG.5, this excessive erasing of the defective column does not cause any problem, as the selection of such a defective column is prohibited by the column gate transistor such as Tsw 3 .
  • the foregoing construction has a drawback in that the writing of information into the redundant memory cell column is not possible in the absence of information 5 about the defective memory cells. More specifically, the writing of data "0" into the memory cells before erasing for avoiding the excessive erasing cannot be conducted for the redundant memory cells. Thereby, the erasing test conducted upon the real memory cells connected to real bit lines BL 1 - BL n inevitably causes an excessive erasing state in the redundant memory cells connected to the redundant bit lines (BL 1 ) CR -(BL 21 ) CR .
  • the circuit of FIG.26 employs a write control circuit 25a that activates the redundant column decoder 24 via an OR gate 25b in response to a redundant selection signal RED ACTIV. Simultaneously, the circuit 25a deactivates the column decoder 15 also via the OR gate as well as via an inverter 25b.
  • the circuit of FIG.26 achieves the usual column redundancy controlled by the defect detection circuit 25 via the OR gate 25b.
  • a control signal W is supplied to the decoders 13, 15 and 24 such that the signal W has a high level state corresponding to the voltage V PP for setting the memory cell transistors in the real memory cell array as well as in the redundant memory cell array to the state ready for writing information.
  • the control signal RED ACTIV is set to the low level state and the writing of the data "0" is achieved into the memory cell transistors in the real memory cell array while prohibiting the wiring of the data "0" into the redundant memory cell arrays.
  • the control signal RED ACTIV is set to the high level state and the writing of the data "0" is conducted into the redundant memory cell transistors while prohibiting the writing into the real memory cell transistors.
  • the erase power supply 22 is activated in response to the erase control signal E, and the flash-erasing of information is achieved for the entirety of the memory cells including the real memory cells and the redundant memory cells.
  • FIG.27 shows an example of the construction of the circuit 25a shown in FIG.26, wherein the circuit includes p-channel MOS transistors 251 and 252 as well as an n-channel MOS transistor 253 connected in series with each other between the two supply voltages V cc and V ss , wherein the transistors 252 and 253 have respective gates connected each other to the supply voltage V cc .
  • the control signal RED ACTIV is supplied to a terminal Pin connected to the drain of the transistor 251 and takes a voltage level V HH that exceeds the supply voltage V CC when the signal RED ACTIV is in the high level state.
  • the p-channel transistor 252 is turned on and the n-channel transistor 253 is turned on and a voltage at the node between the transistors 252 and 253 is supplied to an inverter circuit that includes a series connection of the p-channel transistor 254 and an n-channel transistor 255. Further, the output of the inverter is supplied to a next inverter that includes a series connection of a p-channel transistor 256 and an n-channel transistor 257, and the output control signal to be supplied to the OR gate 25b is obtained at the intermediate node between the transistors 256 and 257.
  • FIG.28 shows a flowchart for separating defective products from good products based upon the foregoing erasing test operation.
  • the writing of data "0" is conducted into the real memory cells in a first step 1 by activating the column address buffer circuit 14 and the column decoder 15.
  • the writing of the data "0" is conducted into the redundant memory cells in a step 2 by activating the redundant decoder 24 via the write control circuit 25a.
  • an erasing process is achieved in a step 3 by activating the erase power supply unit 22. Thereby, the flash erasing of information is achieved for the entirety of the memory cells in the real and redundant memory cell arrays.
  • the result of the flash-erasing process of the step 3 is verified by reading the content of information of the memory cells in the real and redundant memory cell arrays.
  • the device is judged in a step 6 as being a good product.
  • the addresses of the defective memory cells that show the erroneous erasing are written into a memory that is provided in the defect detection circuit 25 in a step 7. Further, a verification process is conducted in a step 8 for verifying the column redundant operation of the device based upon the address of the defective memory cells.
  • step 9 When it is confirmed in a step 9 that the column redundant operation is satisfactory, the step 6 is conducted and the device is identified as being a good product.
  • a step 10 is conducted to achieve the erasing procedure again.
  • the operation of the device is verified is a step 11 by reading the content of the memory cells.
  • the result of the verification process of the step 11 is checked in a discrimination step 12 to discriminate whether the device achieves the satisfactory operation or not. If the result in the step 12 is YES, the step 6 is conducted and the device is identified to be a good product.
  • a step 13 is conducted wherein the device is identified as being a defective product.
  • FIG.29 shows the principle of this device.
  • this device is based upon a concept similar to the concept of the device of FIG.23 and uses a common column decoder for the real memory cell array 11 and redundant memory cell arrays 11 CR1 - 11 CRn .
  • the construction for realizing the column redundancy is substantially simplified.
  • the circuit of FIG.29 is designed for the column redundancy instead of the circuit of FIG.23 that is designed for the testing of the redundant memory cell column and the utility memory cell column, there exists a difference between the circuit of FIG.29 and the circuit of FIG.23 as will be described below.
  • the redundant decoder 24 used in the construction of FIG.5 is no longer used in this device.
  • the column decoder 15 is used commonly for the real memory cell array 11 and the redundant memory cell arrays 11 CR1 - 11 CRn , and the selection of a bit line such as B 1 in the memory cell array 11 causes a simultaneous selection of the bit lines in the redundant memory cell arrays.
  • a switch circuit 16A such the switch circuit 16A is activated in response to a control signal S comp outputted from the defect detection circuit 25.
  • FIG.30 shows the essential part of the circuit of FIG.29, wherein it will be noted that the column decoder 15 includes a number of decoding circuits DC 0 , DC 1 , ... corresponding respectively to the column gate transistors T a , T b , T c , T d , ... , wherein the decoding circuit DC 0 selects the bit line B 0 while the decoding circuit DC 1 selects the bit line B 1 .
  • the transistors T a , T b correspond to the previously described column gate transistors Tsw 1 , ... and form the 16, 16 CR1 , 16 CR2 , ....
  • the defect detection circuit 25 raises the level of one of the control signals SB 0 , SB 1 , ...
  • a decoder such as DC 1 is selectively activated.
  • the bit lines B 1 and B 1s are selected simultaneously.
  • the defect detection circuit 25 supplies the control signal S comp to the switch circuit 16A.
  • the switch circuit 16A includes transfer gate transistors T e and T f wherein the transistors T e and T f are turned on and turned off complementary in response to the control signal S comp .
  • the transistor T e is provided in correspondence to the real memory cell array 11 and the bit lines B 0 , B 1 , ... in the real memory cell array 11 are are connected commonly to the transistor T e via respective column gate transistors T a , T b , ....
  • the redundant bit lines B 0S , B 1S of the redundant memory cell arrays are connected commonly to the transistor T f that corresponds to the redundant memory cell array.
  • FIG.31 shows the construction of the decoding circuit such as DC 0 , wherein it will be noted that p-channel transistors T j , T g , T n , . . , T i are connected in series between the supply voltage V CC and the supply voltage V SS , wherein the transistors T g , T n , . . . T i are supplied with a logic combination of the column address signals and cause a transition to the turned-on state in correspondence to a particular logic combination thereof, while the transistor T j acts as a constant current source and supplies a drive current to a node N where the transistor T j and the transistor T g are connected with each other.
  • the output obtained at the node N as a result of the foregoing decoding action of the transistors T g - T i is supplied to an output inverter that includes a series connection of a p-channel MOS transistor T OUT and an n-channel MOS transistor T OUT ' as usual, wherein there is provided an additional transistor T k such that the transistor T k is connected between the node N and the ground G.
  • the transistor T k is supplied with the foregoing signal S B0 or S B1 from the defect detection circuit 25 at the gate thereof and urges the level of the node N at the low level state in response to the high level state of the control signal S B0 or S B1 , irrespective of the logic combination of the column address signal.
  • the output level of the output inverter is forced to the high level state.
  • the control signals S B0 and S B1 from the defect detection circuit 25 overrides the result of the decoding in the column decoder, and the selection of the redundant bit line occurs irrespective of the decoding operation in the column decoder 15, as long as the column address data specifies a defective memory cell column.
  • FIG.32 shows a modification of the device of FIG.29, wherein the real memory cell array 11 is divided into a plurality of memory cell blocks 11 1 and 11 2 .
  • redundant memory cell blocks 11 CR1 and 11 CR2 are provided.
  • the bit lines in the memory cell block 11 1 are selected by a column gate switch circuit 16 1
  • the bit lines in the memory cell block 11 2 are selected by a column gate switch circuit 16 2
  • the bit lines in the memory cell block 11 CR1 are selected by a column gate switch circuit 16 CR1
  • the bit lines in the memory cell block 11 CR2 are selected by a column gate switch circuit 16 CR2 .
  • a redundant decoder 24A similar to the redundant decoder 24 of FIG.5 is used for activating the column gate switches 16 1 , 16 2 , 16 CR1 and 16 CR2 , wherein the column gate switches 16 1 and 16 2 are controlled by the column decoder as usual.
  • the column gate switches 16 CR1 and 16 CR2 are activated commonly by a control signal SR SEL produced by a redundant decoder 24A.
  • the redundant decoder 24A is supplied with the column address data from the column buffer 14 simultaneously to the column decoder 15 and controls the decoder 15 by supplying a control signal S INH such that the operation of the decoder 15 is prohibited when there exist a bit line in the real memory cell 11 1 or 11 2 and also a bit line in the redundant memory cell 11 CR1 and 11 CR2 in correspondence to a given column address
  • the decoder 24A prohibits the operation of the decoder 15 and selects redundant bit lines in the memory cell arrays 11 CR1 and 11 CR2 .
  • the reading of information is achieved either from the real memory cell array or from the redundant memory cell array.
  • the reading is achieved either from the memory cell array 11 1 or 11 CR1 , and the information thus read out is supplied to the transistor T e that forms a part of the switch circuit 16A.
  • the reading of information is achieved either from the memory cell array 11 2 or from the redundant memory cell array 11 CR2 and the information thus read out is supplied to the transistor T f included in the switch circuit 16A.
  • the decoder 24A further produces control signals SR 1 and SR 2 and activates either the transistor T e or the transistor T f in response to the logic combinations of the signals SR 1 and SR 2 via a control circuit 24B.
  • control circuit 24B As a result, reading of information is achieved selectively from either of the memory cell arrays 11 1 , 11 2 , 11 CR1 and 11 CR2 .
  • FIG.33 shows the construction of the circuit 24B.
  • the circuit 24B includes a NOR gate 241 and a NAND gate 242 connected in series wherein the supply voltage V SS is supplied to one input terminal of the NOR gate 241 while the most significant bit A MSB of the column address data is supplied to the other input terminal.
  • the output of the NAND gate 242 is supplied to a NOR gate 243, wherein the NOR gate 243 is supplied with the control signal SR 1 at the other input terminal. Further, the output of the NOR gate 243 is supplied to a first input terminal of a NOR gate 244 that is supplied also with the control signal SR 2 at the other input terminal.
  • the output of the NOR gate 244 is supplied to the transistor T e as a control signal SEL and further to the transistor T f via an inverter 245 as a control signal SELx.
  • the output signals SEL and SELx are produced as a result of the logic combination of the signals A MSB , SR 1 and SR 2 .
  • the signal SEL takes the same logic level as the signal A MSB when the signals SR 1 and SR 2 both have the low level state in correspondence to the non-redundant operation.
  • the logic level of the output signal SEL is urged to the high level state when the signal SR 1 has the high level state. Further, the signal SEL is urged to the low level state when the signal SR 2 has the high level state.
  • the present modification as described with reference to FIGS.32 and 33 is also effective for simplifying the construction of the memory device by controlling the redundant memory cell arrays 11 CR1 and 11 CR2 by the same control signal SR SEL produced by the same decoder circuit 24A.
  • V H very high voltage
  • the application of such a high voltage to the n + -type source region tends to invite a breakdown at the p-n junction between the source region and the substrate.
  • the application of such a very large voltage to the source region tends to induce a depletion region in the substrate immediately under the gate insulation film, and the large electric field associated with such a depletion region may cause to flow a tunneling current from the valence band to the conduction band.
  • the same goal as the FIG. 11 embodiment is achieved by applying simultaneously a positive voltage to the substrate and a negative voltage to the control gate electrode, when erasing information, with the same magnitude such that no extraordinary large voltage appears between the active parts of the memory cell transistors as well as the peripheral transistors forming the peripheral circuit.
  • FIG.34 shows the foregoing principle of the flash memory as well as the device structure that is tailored for implementing the foregoing principle.
  • the flash memory is constructed on a p-type substrate 110 that is defined with a memory cell region wherein memory transistors A and B are formed and a peripheral region wherein a peripheral transistor is formed.
  • the memory cell region includes n + -type diffusion regions 126a and 128a respectively serving for the source and drain of the memory cell transistor A and diffusion regions 126b and 128b respectively serving for the source and drain of the memory cell transistor B.
  • the memory cell transistors A and B are isolated from each other by a field oxide region 116, and a gate insulation film 118 covers the surface of the device region for the transistors A and B as usual in MOS transistors.
  • a floating gate electrode 120a is provided in correspondence to the memory cell transistor A, while a floating gate electrode 120b is provided on the gate insulation film 118 in correspondence to the memory cell transistor B.
  • capacitor insulation films 122a and 122b are formed respectively, and control gate electrodes 124a and 124b are provided respectively on the capacitor insulation films 122a and 122b.
  • a p-type well 114 surrounded by an external well 112 is formed in the substrate 110 in correspondence to the peripheral region, and n + -type diffusion regions 132 and 134 are formed in the well 114 as the source and drain of the peripheral transistor.
  • the gate insulation film 118 is formed also on the surface of the substrate 110 in correspondence to the peripheral transistor and a gate electrode 130 is provided thereon.
  • the present device When erasing information from the memory cell transistor A, for example, the present device applies a gate voltage of -10 volts to the control gate electrode 124a while simultaneously applies a substrate voltage of +10 volts. Thereby, a voltage difference of 20 volts is formed between the control gate electrode 124a and the substrate 110, and the electrons accumulated in the floating gate 120a are expelled to the substrate 110 in the form of the Fowler-Nordheim tunnel current. In order to avoid the unwanted erasing of information, a positive voltage of +10 volts is applied simultaneously to the control gate 124b of the memory cell transistor. Thereby, it will be noted that the voltage difference between the control gate 124b and the substrate 110 becomes zero.
  • the voltage level of the substrate 110 increases positively also in the peripheral region if the substrate of the peripheral region is not isolated from the rest of the part of the substrate in the form of double well structure shown in FIG.34. There, the positive voltage level applied to the p-type substrate inevitably induces a forward biasing at the p-n junction between the substrate and the diffusion regions 132, 134.
  • the present device avoids this problem of adversary forward biasing by providing an n-type well 112 in the substrate 110 in correspondence to the peripheral region and further by forming a p-type well 114 within the n-type well 112. Thereby, the diffusion regions 132 and 134 are formed within the p-type well 114.
  • a positive voltage set equal to the positive voltage applied to the substrate 112 is applied to the n-type well 112 such that there occurs no substantial biasing between the p-type substrate 110 and the n-type well. Further, the voltage level of the p-type well 114 is held at zero volt. Thereby, the p-n junction at the interface between the n-type well 112 and the p-type well 114 are reversely biased, and the depletion region developing along the p-n junction effectively isolates the p-type well 114 from the p-type substrate 110.
  • the structure of FIG.34 enables the effective erasing of information without providing excessive electric stress to any part of the device.
  • the reading and writing of information is achieved similarly to the conventional process shown in FIG.2. Further, when erasing information, one may apply the same positive voltage as the substrate voltage to the source and drain regions of the memory cell transistor.
  • FIG.35 is a modification of the device of FIG.34, wherein the memory cell region is isolated from the peripheral region by a double well isolation structure.
  • the double well includes an outer n-type well 136 and an inner p-type well 138, and the diffusion regions of the memory cell transistors A and B are all formed within the inner p-type well 138.
  • the rest of the feature is identical with the device of FIG.34, further description of the structure of FIG.35 will be omitted.
  • the n-type well 112 is formed in the substrate 110 in correspondence to the peripheral region by means of an ion implantation process of an n-type dopant such as As or P followed by a thermal annealing process.
  • the p-type well 114 is formed in the n-type well 112 by means of an ion implantation process of a p-type dopant such as B.
  • the surface of the substrate 110 is protected by an oxidation resistant mask (not shown) such as silicon nitride in correspondence to the region where the active part of the device is formed, and the substrate 110 thus masked is subjected to a thermal oxidation process conducted in a wet O 2 environment. Thereby, the field oxide region 16 is formed.
  • the mask is removed and the gate oxide film 118 is formed by a thermal oxidation process conducted in a dry O 2 environment. Thereby, the structure shown in FIG.36(B) is formed.
  • a first polysilicon layer is deposited and patterned subsequently to form the floating gate electrodes 120a and 120b respectively in correspondence to the memory cell transistors A and B as shown in FIG.36(C). Further, the structure of FIG.36(C) is subjected to a thermal oxidation process to form the capacitor insulation films 122a and 122b on the floating electrodes 120a and 120b, respectively, and a second polysilicon layer 124 is deposited further thereon. Thereby, the structure shown in FIG.36(D) is obtained.
  • the polysilicon layer 124 is patterned to form the control gate electrodes 124a and 124b as well as the gate electrode 130.
  • ion implantation of the n-type dopant such as As or P is conducted to forn the diffusion regions 126a, 126b, 128a and 128b while using the gate structure as a self-alignment mask in each of the memory cell region and the peripheral region.
  • a laminated structure By employing such a laminated structure, it is possible to reduce the thickness of the capacitor insulation film without sacrificing the reliability and anti-leak characteristics of the device. Thereby, an efficient capacitor coupling is achieved between the control electrode and the floating gate electrode.
  • the silicon oxide film formed on the polysilicon floating gate shown in FIG.1 tends to form pinholes when the thickness is reduced due to the effect of the grain boundaries in the gate electrode.
  • By covering the thin silicon oxide film by a silicon nitride film and form a thin silicon oxide film further on the silicon nitride film one can successfully eliminate the leak from the floating gate while reducing the thickness of the capacitor insulation film.
  • FIG.37 shows the structure of such a memory cell transistor that has the laminated structure for the capacitor insulation film 4.
  • the capacitor insulation film 4 includes a silicon oxide film 4a formed directly on the floating gate electrode 3, a silicon nitride film 4b deposited on the silicon oxide film 4a, and a silicon oxide film 4c formed on the silicon nitride film 4b.
  • the power supply unit 22 as well as the power supply units 22 1 , . . . may be a switching circuit for switching the source voltage between a high level voltage such as +12 volts and a low level voltage such as +5 volts, instead of the voltage generator circuit that generates the high voltage output and the low voltage output.
  • a high level voltage such as +12 volts
  • a low level voltage such as +5 volts
  • the power supply unit merely switches the output voltage in response to a control signal.

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Read Only Memory (AREA)
  • Semiconductor Memories (AREA)
  • For Increasing The Reliability Of Semiconductor Memories (AREA)
  • Non-Volatile Memory (AREA)

Claims (11)

  1. Un dispositif de mémoire à semiconducteur à effacement instantané, comprenant :
    un réseau de cellules de mémoire (11) comprenant un ensemble de transistors de cellules de mémoire (11a), chacun de ces transistors de cellules de mémoire comprenant : une grille flottante isolée (3) formée sur un substrat semiconducteur (1), en étant séparée de celui-ci, pour enregistrer de l'information sous la forme de charges électriques; une pellicule d'isolation de grille (2) formée sur une surface principale supérieure du substrat semiconducteur (1), pour séparer la grille flottante (3) vis-à-vis du substrat semiconducteur; une région de canal définie dans le substrat semiconducteur, en correspondance avec la grille flottante (3); une région de source (6) et une région de drain (7) définies dans le substrat semiconducteur de part et d'autre de la grille flottante (3), la région de source (6) injectant des porteurs dans la région de canal de façon que ces porteurs soient transportés le long de la région de canal, tandis que la région de drain (7) collecte des porteurs qui ont été injectés dans la région de canal à la région de source, et qui ont été transportés à travers la région de canal; et une électrode de commande (5) formée sur la grille flottante (3), en étant séparée de celle-ci par une pellicule d'isolation de condensateur (4), pour commander une injection de porteurs de la région de canal vers la grille flottante (3), à travers la pellicule d'isolation de grille (4);
    des moyens d'adressage (12-16) recevant des données d'adresse pour sélectionner un transistor de cellule de mémoire (11a) dans le réseau de cellules de mémoire (11);
    des moyens d'écriture (19) pour écrire de l'information dans le transistor de cellule de mémoire sélectionné;
    des moyens de lecture (20) pour lire de l'information dans le transistor de cellule de mémoire sélectionné; et
    des moyens d'effacement (22) pour effacer de l'information, de manière simultanée, dans un ensemble de transistors de cellules de mémoire (11a) qui sont inclus dans le réseau de cellules de mémoire (11), ces moyens d'effacement effaçant de l'information en éliminant des charges électriques à partir des électrodes de grille flottante des transistors de cellules de mémoire, en faisant circuler un courant tunnel à travers la pellicule d'isolation de grille;
    caractérisé en ce que les moyens d'effacement (22) comprennent des moyens de sélection de conducteur de mot pour sélectionner un conducteur de mot; et en ce que des moyens de commande d'effacement (23) sont incorporés pour commander les moyens de sélection de conducteur de mot, en appliquant une tension de grille (VG) à l'électrode de commande (5), avec une polarité et une valeur absolue suffisantes pour faire circuler le courant tunnel des charges électriques à travers la pellicule d'isolation de grille (2).
  2. Un dispositif de mémoire à semiconducteur à effacement instantané selon la revendication 1, dans lequel la polarité de la tension de grille (VG) est fixée de façon à être identique à la polarité des charges électriques qui sont stockées dans la grille flottante (3).
  3. Un dispositif de mémoire à semiconducteur à effacement instantané selon la revendication 2, dans lequel les moyens de commande d'effacement (23) appliquent en outre une tension de polarisation d'effacement (VL) au substrat, avec une polarité opposée à la polarité de la tension de grille (VG).
  4. Un dispositif de mémoire à semiconducteur à effacement instantané selon la revendication 3, dans lequel la tension de polarisation d'effacement (VL) a une valeur absolue notablement inférieure à la valeur absolue de la tension de grille (VG).
  5. Un dispositif de mémoire à semiconducteur à effacement instantané selon la revendication 3, dans lequel la tension de polarisation d'effacement (VL) a une valeur absolue pratiquement égale à la valeur absolue de la tension de grille (VG).
  6. Un dispositif de mémoire à semiconducteur à effacement instantané selon l'une quelconque des revendications précédentes, dans lequel le réseau de cellules de mémoire comprend : un réseau de cellules de mémoire principal (11) et un réseau de cellules de mémoire redondant, comprenant chacun un ensemble des transistors de cellules de mémoire (11a), le réseau de cellules de mémoire principal comprenant un ensemble de conducteurs de mot principaux (WL1, WL2) en correspondance avec l'ensemble de transistors de cellules de mémoire disposés en un ensemble de lignes, le réseau de cellules de mémoire redondant comprenant au moins un conducteur de mot redondant (WL3) en correspondance avec l'ensemble de transistors de cellules de mémoire disposés en une ou plusieurs lignes; les moyens de sélection de conducteur de mot (22) comprenant : des moyens d'adressage (12, 13) auxquels sont appliquées des données d'adresse de ligne qui font partie des données d'adresse, pour sélectionner un conducteur de mot dans les moyens de mémoire principaux; des moyens de discrimination (34) qui reçoivent les données d'adresse de ligne pour déterminer si les données d'adresse de ligne sélectionnent un conducteur de mot défectueux dans le réseau de cellules de mémoire principal; et des moyens d'adressage redondants (35) recevant les données d'adresse de ligne et un signal de sortie des moyens de discrimination (34) pour sélectionner un conducteur de mot redondant (WL3) sous la dépendance du signal de sortie des moyens de discrimination.
  7. Un dispositif de mémoire à semiconducteur à effacement instantané selon l'une quelconque des revendications précédentes, dans lequel la pellicule d'isolation de condensateur (4) a une structure multi-couche comprenant une couche de nitrure de silicium (4b) intercalée entre une paire de couches d'oxyde de silicium (4a, 4c).
  8. Un dispositif de mémoire à semiconducteur à effacement instantané selon l'une quelconque des revendications précédentes, dans lequel les moyens de commande d'effacement (23) appliquent en outre une tension de polarisation d'effacement (VE) à la source, avec une polarité opposée à la polarité de la tension de grille (VG) et une valeur absolue identique à celle de la tension de grille (VG).
  9. Un dispositif de mémoire à semiconducteur à effacement instantané selon l'une quelconque des revendications précédentes, dans lequel les moyens de commande d'effacement (23) appliquent en outre une tension de polarisation d'effacement au drain avec une polarité opposée à la polarité de la tension de grille et une valeur absolue identique à celle de la tension de grille.
  10. Un dispositif de mémoire à semiconducteur à effacement instantané selon la revendication 6, dans lequel le réseau de cellules de mémoire comprend un ensemble de conducteurs de bit (BL1, BL2, BL3) s'étendant en commun dans le réseau de cellules de mémoire principal (11) et dans le réseau de cellules de mémoire redondant, de façon que chaque conducteur de bit s'étende à travers le réseau de cellules de mémoire principal et en outre à travers le réseau de cellules de mémoire redondant, chacun des conducteurs de bit étant connecté à un drain d'un ensemble de transistors de cellules de mémoire qui sont disposés de façon à former une colonne, les sources des transistors de cellules de mémoire étant connectées en commun à une unité d'alimentation (22) pendant l'effacement d'information.
  11. Un dispositif de mémoire à semiconducteur à effacement instantané selon l'une quelconque des revendications 6 à 10, dans lequel le dispositif de mémoire à semiconducteur à effacement instantané comprend en outre un second réseau de cellules de mémoire redondant (11CR) comprenant un ensemble de conducteurs de bit (BLR), chacun d'eux étant connecté à un ensemble de transistors de cellules de mémoire (11a), les transistors de cellules de mémoire dans le second réseau de cellules de mémoire redondant (11CR) étant sélectionnés lorsque le transistor de cellule de mémoire qui est sélectionné dans le réseau de cellules de mémoire principal (11) est défectueux.
EP92310606A 1991-11-20 1992-11-20 Dispositif de mémoire à semi-conducteurs effaçable par bloc ayant un fonctionnement amélioré Expired - Lifetime EP0543656B1 (fr)

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EP97119754A EP0841667B1 (fr) 1991-11-20 1992-11-20 Dispositif de mémoire à semi-conducteurs effaçable en mode flash avec fiabilité améliorée
EP01109363A EP1126474B1 (fr) 1991-11-20 1992-11-20 Dispositif de mémoire à semi-conducteurs
EP01109361A EP1126472B1 (fr) 1991-11-20 1992-11-20 Dispositif de mémoire effaçable flash à semi-conducteurs
EP01109362A EP1126473B1 (fr) 1991-11-20 1992-11-20 Dispositif de mémoire à semi-conducteurs

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JP304894/91 1991-11-20
JP30489491A JP3144002B2 (ja) 1991-11-20 1991-11-20 フラッシュ・メモリ
JP31668291A JP2625298B2 (ja) 1991-11-29 1991-11-29 不揮発性半導体記憶装置
JP316682/91 1991-11-29
JP31945191A JP3106624B2 (ja) 1991-12-03 1991-12-03 フラッシュ・メモリ
JP319451/91 1991-12-03
JP347343/91 1991-12-27
JP34734391A JP3543973B2 (ja) 1991-12-27 1991-12-27 半導体記憶装置及びその情報消去方法
JP4216/92 1992-01-13
JP421692A JP3116505B2 (ja) 1992-01-13 1992-01-13 フラッシュ・メモリ
JP6173092A JP2689808B2 (ja) 1992-03-18 1992-03-18 不揮発性半導体記憶装置
JP61730/92 1992-03-18
JP21038092A JP3201838B2 (ja) 1992-08-06 1992-08-06 半導体記憶装置
JP210380/92 1992-08-06
JP249958/92 1992-09-18
JP24995892A JPH06103798A (ja) 1992-09-18 1992-09-18 半導体記憶装置
JP31047292A JP3360855B2 (ja) 1992-11-19 1992-11-19 一括消去型不揮発性半導体記憶装置およびその試験方法
JP310472/92 1992-11-19

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EP01109362A Expired - Lifetime EP1126473B1 (fr) 1991-11-20 1992-11-20 Dispositif de mémoire à semi-conducteurs
EP97119754A Expired - Lifetime EP0841667B1 (fr) 1991-11-20 1992-11-20 Dispositif de mémoire à semi-conducteurs effaçable en mode flash avec fiabilité améliorée
EP01109363A Expired - Lifetime EP1126474B1 (fr) 1991-11-20 1992-11-20 Dispositif de mémoire à semi-conducteurs
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EP97119754A Expired - Lifetime EP0841667B1 (fr) 1991-11-20 1992-11-20 Dispositif de mémoire à semi-conducteurs effaçable en mode flash avec fiabilité améliorée
EP01109363A Expired - Lifetime EP1126474B1 (fr) 1991-11-20 1992-11-20 Dispositif de mémoire à semi-conducteurs
EP01109361A Expired - Lifetime EP1126472B1 (fr) 1991-11-20 1992-11-20 Dispositif de mémoire effaçable flash à semi-conducteurs

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EP1126472A1 (fr) 2001-08-22
US5910916A (en) 1999-06-08
US6014329A (en) 2000-01-11
DE69233305T2 (de) 2004-07-08
EP1126473A1 (fr) 2001-08-22
DE69232950D1 (de) 2003-04-10
US5761127A (en) 1998-06-02
EP1126473B1 (fr) 2004-02-18
US5835408A (en) 1998-11-10
EP0543656A3 (en) 1994-09-21
DE69227011D1 (de) 1998-10-22
EP1126474B1 (fr) 2003-03-05
DE69232949D1 (de) 2003-04-10
DE69232949T2 (de) 2003-08-28
DE69232470T2 (de) 2002-07-11
EP0543656A2 (fr) 1993-05-26
EP0841667B1 (fr) 2002-03-06
DE69232470D1 (de) 2002-04-11
DE69232950T2 (de) 2003-08-28
EP0841667A3 (fr) 1999-06-16
DE69227011T2 (de) 1999-02-18
EP1126474A1 (fr) 2001-08-22
US5835416A (en) 1998-11-10
US5870337A (en) 1999-02-09
EP1126472B1 (fr) 2003-03-05
EP0841667A2 (fr) 1998-05-13
DE69233305D1 (de) 2004-03-25

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